The purpose of this research is to investigate the possible function of the nervus terminalis, in a representative mammal, as an intermediary in the relay of chemical signals from the external environment to the neuroendocrine centers of the brain and to determine if it acts alone or in concert with the olfactory, vomeronasal and/or trigeminal nerves. The nervus terminalis is the only neural component of the mammalian nose which projects directly from the nose to the septal and preoptic areas of the forebrain, regions which have been implicated in the reception and coordination of stimuli that evoke specific behavioral and hormonal changes relevant to reproductive function. It is the least studied of the "olfactory" systems because of difficulty in distinguishing it from the olfactory and vomeronasal nerves. The recent finding of immunoreactive luteinizing hormone (LHRH) in the nerve fiber bundles and processes and in many of the ganglion cells (including the ganglion terminale) associated with this nerve in several species including the guinea pig, hamster, rat and teleost fishes now makes an anatomical distinction feasible and provides a tool for investigating the function of this nerve. The specific objectives of this investigation are (I) a chemical (LHRH; other possible hormones and/or neurotransmitters) and morphometric characterization of the nervus terminalis by immunocytochemistry, retrograde tracing and light microscopy against which experimental changes can be evaluated; (II) an investigation of the function of the LHRH systems of the nervus terminalis in the adult rat by stimulus-response testing with internal (hormonal) and external (chemical, including sexually relevant and thermal) stimuli, electrophysiological recording and radio frequency lesions to determine the specificity of the stimulus for the nervus terminalis and/or related olfactory systems; (III) a study by immunocytochemistry of the development of the LHRH system of the nervus terminalis in the fetal and neonatal rat in relation to the initial appearance of this hormone in other areas of the brain and luteinizing hormone (LH) in the anterior pituitary and investigation of the possible function of this system in development of the central nervous system-pituitary-gonadal axis.